In the field of machine tools numerical controls which can be adapted to a single machine at a time have been developed up to now. Each machine, therefore, has its own numerical control, consisting of an automaton comprising a digital computer and a monitoring unit and having a fixed program. With this type of device one cannot in general monitor and operate more than two spindles simultaneously and therefore it does not make it possible to carry out more than two operations at a time. The cost of such machines is therefore relatively high since they each have their own automaton.
Such machine tools are known and described for instance in U.S. Pat. No. 4,124,887 and French Patent No. 2 228 247, in accordance with which there is present, incorporated in each machine tool, a computer which is specific to them, and their own tape reader which controls said machine and in which only the monitoring is effected by a centralized computer.
Since the twenty years that these numerical controls have been developed their efficiency has improved greatly, particularly during the last few years in which microprocessors have been introduced as numerical control, but the general philosophy of these machines has still remained limited to the concept of unit machine tools each having its own automaton. Therefore, in a shop equipped with several machine tools, for instance twenty machine tools, each of these tools has its own automaton which requires the presence of a large number of skilled workers. Furthermore, the present machines with their automatons are very expensive despite the advances made in microprocessors; they are generally reserved, in order to have sufficient output, to the manufacture of parts of very high quality and therefore for limited series and in principle it is not profitable to use them for the manufacture of large series of parts.
Up to now, one never had the idea of centralizing all the numerical controls in a single computer, despite the fact that there is at present a need for such streamlining, as indicated above. The reasons for this lack can be imputed, on the one hand, to the fact that the field of machine tools is a rather self-contained traditional field having few relations with the field of electronics, and, on the other hand, it was believed that numerous difficulties in production had to be surmounted.
At first sight one could imagine that with the arrival of microprocessors on the market these microprocessors would lend themselves to such centralization of the control. Unfortunately, this is not possible and if anyone has tried to apply microprocessors for this he will certainly have come up against great difficulties since, due to their configuration, microprocessors do not lend themselves to the effecting of such centralization.